File system operation handling during cutover and steady state

ABSTRACT

Techniques are provided for synchronous replication based cutover. An asynchronous replication process is executed to perform asynchronous incremental transfers of data of a storage object from a first computing environment to a replicated storage object at a second computing environment until a cutover criteria is met. A synchronous replication process is executed to synchronously replicate operations, targeting the storage object, to the replicated storage object based upon the cutover criteria being met. A cutover is performed to direct operations from targeting the storage object to targeting the replicated storage object based upon the synchronous replication process reaching a steady state of synchronous replication for sub-objects of the storage object, where operations are committed to both the storage object and the replicated storage object.

RELATED APPLICATIONS

This application claims priority to and is a continuation of U.S. patentapplication Ser. No. 16/191,582, titled “SYNCHRONOUS REPLICATION BASEDCUTOVER ENGINE” and filed on Nov. 15, 2018, which claims priority toIndia Patent Application, titled “SYNCHRONOUS REPLICATION BASED CUTOVERENGINE”, filed on Aug. 2, 2018 and accorded Indian Application No.:201841029051, which are incorporated herein by reference.

BACKGROUND

Many storage systems may implement data replication and/or otherredundancy data access techniques for data loss protection andnon-disruptive client access. For example, a first computing device maybe configured to provide clients with primary access to data storedwithin a first storage device and/or other storage devices. A secondcomputing device may be configured as a backup for the first computingdevice in the event the first computing device fails. Data may bereplicated from the first computing device to the second computingdevice. In this way, the second computing device can provide clientswith access to replicated data in the event the first computing devicefails.

Storage virtual machines may be used to manage storage (e.g., aplurality of volumes stored across one or more nodes of a cluster) andprovide clients with access to such storage. It may be beneficial tomigrate a storage virtual machine from one cluster to another cluster,such as for load balancing. Unfortunately, migrating the storage virtualmachine is very disruptive to clients. This is because client access tostorage hosted by the storage virtual machine is quiesced (blocked),which increases client I/O latency, can result in applications relyingon data within the storage to time out or experience errors, etc.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in which an embodiment of the invention may be implemented.

FIG. 2 is a component block diagram illustrating an example data storagesystem in which an embodiment of the invention may be implemented.

FIG. 3 is a flow chart illustrating an example method for synchronousreplication based cutover.

FIG. 4A is a component block diagram illustrating an example system forsynchronous replication based cutover, where asynchronous replication isperformed.

FIG. 4B is a component block diagram illustrating an example system forsynchronous replication based cutover, where synchronous replication isperformed.

FIG. 4C is a component block diagram illustrating an example system forsynchronous replication based cutover, where a cutover phase isperformed.

FIG. 4D is a component block diagram illustrating an example system forsynchronous replication based cutover, where client access is cut overto a replicated storage object.

FIG. 5 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

FIG. 6 is a component block diagram illustrating an example computingenvironment in which an embodiment of the invention may be implemented.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

Many technological processes for migrating storage objects, such asvolumes and storage virtual machines, are disruptive to clients. Thesemigration processes may be limited to performing asynchronous transfersof data from a source storage object to a destination storage object.These asynchronous transfers replicate incremental changes to data ofthe source storage object to the destination storage object. Once theasynchronous transfers are complete, I/O from clients to the sourcestorage object are fenced/quiesced (blocked). This results insignificant client latency for applications and computers that replyupon access to the data of the source storage object because I/O isblocked, such as failed or queued for later execution. Thus, clients mayexperience higher latency due to fencing/quiescing of I/O during acutover period where clients are cut over from being able to access thesource storage object to being able to access the destination storageobject. This can cause the applications and computers to time out,crash, or have other operational issues and downtime.

Accordingly, these migration processes are improved by performingnon-disruptive migration that reduces the disruptiveness and clientlatency associated with migrating storage objects. This improvement isachieved by additionally utilizing a synchronous replication process inthe migration process. Using synchronous replication has the advantageof keeping client experienced latency to a significantly lower number.Also, synchronous replication is used to achieve a successfulnon-disruptive migration of a storage virtual machine that is acollection of volumes.

In an embodiment, an asynchronous replication process is performed toasynchronously replicate incremental changes to data of a storage objectto a replicated storage object. For example, changes to data withinvolumes of a storage virtual machine stored across a plurality of nodesof a first cluster are asynchronously replicated to replicated volumesof a replicated storage virtual machine at a second cluster. This isdone as part of a non-disruptive migration process to migrate thestorage virtual machine from the first cluster to the second cluster,such as to improve performance or to more efficiently utilize storagecapacity (e.g., the second cluster may have more available storageresources and/or processing resources).

The asynchronous incremental transfers are performed until a cutovercriteria is met. The cutover criteria can be defined as a set amount oftime or a certain amount of data remaining to be replicated.Accordingly, a synchronous replication process is executed in responseto the cutover criteria being met. The synchronous replication processis executed to synchronously replicate operations targeting the storageobject. The operations are executed upon the storage object and arereplicated to create replicated operations that are transmitted to thesecond cluster for execution upon the replicated storage object. Inresponse to receiving an acknowledgment message from the second clusterthat the replicated operation was received, an acknowledgement ofsuccessfully completion of the operation is returned to a clientcomputing device that generated the operation.

Transmission of the acknowledgement message is based upon receipt of thereplicated operation by the second cluster for subsequent execution uponthe replicated storage object and not commitment of the replicatedoperation, and thus the client computing device experiences low latency.Otherwise, the client computing device would experience higher latencybecause the acknowledgement message of success would not be sent to theclient computing device until after the replicated operation iscommitted. This also allows the second cluster to queue replicatedoperations so that the replicated operations can be committed to storagein a manner that guarantees dependent write order consistency of whatorder the first cluster executed corresponding operations. For example,a first write operation writes data A to the storage object and a secondwrite operation overwrites data A with data B. If the second clusterexecutes a replication of the second write operation before areplication of the first write operation, then data inconsistency willresults because the second cluster will now store data A while the firstcluster stores data B.

Once all sub-objects of the storage object (e.g., each volume of thestorage virtual machine) are in a steady state of synchronousreplication with the replicated storage object (e.g., operations andreplicated operations are being committed to storage), a cutover phaseis performed. The cutover phase is performed to switch clients fromaccessing the storage object to accessing the replicated storage object.A cutover window of the cutover phase where client I/O is quiesced isshorter than convention migration techniques because cutover can bequickly performed since the storage object and the replicated storageobject are in a steady synchronous state so less time is spentsynchronizing any remaining data. Even though both copies aresynchronized (the storage object and the replicated storage object arein sync), there are latency improvements/benefits because there aremerely a few pending I/Os on the replicated storage object (thesecondary copy) that will have to be drained during the cutover phase.During the cutover phase, these I/Os are drained, and thus this is theonly time period where I/O is quiesced because synchronous replicationwas used as an underlying engine for migration.

During the cutover phase, client I/O is quiesced, and a final drain isperformed to complete any pending in-flight operations and replicatedoperations (e.g., inflight operations comprising operations notcommitted yet to both the storage object and the replicated storageobject). Any additional filesystem metadata, such as network file system(NFS) lock data, a replay cache for non-idempotent operations, etc., istransferred to the second cluster. Once complete, clients are redirectedto the replicated storage object. In contrast, existing migrationtechniques would have to perform additional data replication in order toplace the storage object and the replicated storage object in aconsistent state. This increases client latency and adversely affectsthroughput for clients. Accordingly, synchronous replication isperformed before cutover in order to reduce latency and improve clientthroughput because the time client I/O is quiesced is reduced due tohaving little to no additional data to replicate (e.g., merely in-flightoperations need to be drained and filesystem metadata need to be copiedover).

This non-disruptive migration technique also provides other improvementsover existing migration techniques. For example, existing migrationtechniques may be unable to migrate more than a single volume betweenclusters in a predictable manner. In contrast, this non-disruptivemigration technique can migrate a storage virtual volume of a pluralityof volumes stored across multiple nodes in a predictable manner. Eventhough each volume is independent of one another and could havedifferent change rates of data, migration is performed in a predictablemanner because synchronous replication places the storage volumes andreplicated storage volumes in steady state of synchronous replicationbefore cutover. This also allows for a more relaxed cutover criteria tobe specified. Otherwise, existing migration techniques, using merelyasynchronous replication, must comply with stringent cutover criteriathat can result in failed cutover attempts that do not complete within atime limit set by such stringent cutover criteria.

To provide for non-disruptive migration, FIG. 1 illustrates anembodiment of a clustered network environment 100 or a network storageenvironment. It may be appreciated, however, that the techniques, etc.described herein may be implemented within the clustered networkenvironment 100, a non-cluster network environment, and/or a variety ofother computing environments, such as a desktop computing environment.That is, the instant disclosure, including the scope of the appendedclaims, is not meant to be limited to the examples provided herein. Itwill be appreciated that where the same or similar components, elements,features, items, modules, etc. are illustrated in later figures but werepreviously discussed with regard to prior figures, that a similar (e.g.,redundant) discussion of the same may be omitted when describing thesubsequent figures (e.g., for purposes of simplicity and ease ofunderstanding).

FIG. 1 is a block diagram illustrating the clustered network environment100 that may implement at least some embodiments of the techniquesand/or systems described herein. The clustered network environment 100comprises data storage systems 102 and 104 that are coupled over acluster fabric 106, such as a computing network embodied as a privateInfiniband, Fibre Channel (FC), or Ethernet network facilitatingcommunication between the data storage systems 102 and 104 (and one ormore modules, component, etc. therein, such as, nodes 116 and 118, forexample). It will be appreciated that while two data storage systems 102and 104 and two nodes 116 and 118 are illustrated in FIG. 1, that anysuitable number of such components is contemplated. In an example, nodes116, 118 comprise storage controllers (e.g., node 116 may comprise aprimary or local storage controller and node 118 may comprise asecondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, In an embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while In an embodiment a clustered network caninclude data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets, a Storage Area Network (SAN) protocol, such as Small ComputerSystem Interface (SCSI) or Fiber Channel Protocol (FCP), an objectprotocol, such as S3, etc. Illustratively, the host devices 108, 110 maybe general-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more storagenetwork connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in theclustered network environment 100 can be a device attached to thenetwork as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the clustered network environment 100, nodes 116, 118can comprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise network modules 120, 122 and disk modules 124, 126. Networkmodules 120, 122 can be configured to allow the nodes 116, 118 (e.g.,network storage controllers) to connect with host devices 108, 110 overthe storage network connections 112, 114, for example, allowing the hostdevices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, the network module 120 of node 116 can access asecond data storage device by sending a request through the disk module126 of node 118.

Disk modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, disk modules 124, 126 communicate with the data storage devices128, 130 according to the SAN protocol, such as SCSI or FCP, forexample. Thus, as seen from an operating system on nodes 116, 118, thedata storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the clustered network environment100 illustrates an equal number of network and disk modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and disk modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and disk modules. That is, differentnodes can have a different number of network and disk modules, and thesame node can have a different number of network modules than diskmodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the storage networking connections 112, 114. As anexample, respective host devices 108, 110 that are networked to acluster may request services (e.g., exchanging of information in theform of data packets) of nodes 116, 118 in the cluster, and the nodes116, 118 can return results of the requested services to the hostdevices 108, 110. In an embodiment, the host devices 108, 110 canexchange information with the network modules 120, 122 residing in thenodes 116, 118 (e.g., network hosts) in the data storage systems 102,104.

In an embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. In an example, a disk array can include alltraditional hard drives, all flash drives, or a combination oftraditional hard drives and flash drives. Volumes can span a portion ofa disk, a collection of disks, or portions of disks, for example, andtypically define an overall logical arrangement of file storage on diskspace in the storage system. In an embodiment a volume can comprisestored data as one or more files that reside in a hierarchical directorystructure within the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the clustered network environment 100, the host devices 108, 110 canutilize the data storage systems 102, 104 to store and retrieve datafrom the volumes 132. In this embodiment, for example, the host device108 can send data packets to the network module 120 in the node 116within data storage system 102. The node 116 can forward the data to thedata storage device 128 using the disk module 124, where the datastorage device 128 comprises volume 132A. In this way, in this example,the host device can access the volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the storage networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the node 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The node 118 can forward the data to the data storagedevice 130 using the disk module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that replay of metadata and data operations may beimplemented within the clustered network environment 100. In an example,operations may be executed at node 116 and replayed at node 118. It maybe appreciated that replay of metadata and data operations may beimplemented for and/or between any type of computing environment, andmay be transferrable between physical devices (e.g., node 116, node 118,a desktop computer, a tablet, a laptop, a wearable device, a mobiledevice, a storage device, a server, etc.) and/or a cloud computingenvironment (e.g., remote to the clustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The data storage system 200 comprises a node202 (e.g., nodes 116, 118 in FIG. 1), and a data storage device 234(e.g., data storage devices 128, 130 in FIG. 1). The node 202 may be ageneral purpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A host device205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provide access to files and/or other datastored on the data storage device 234. In an example, the node 202comprises a storage controller that provides client devices, such as thehost device 205, with access to data stored within data storage device234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The data storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The host device 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrievedby the storage adapter 214 and, if necessary, processed by the one ormore processors 204 (or the storage adapter 214 itself) prior to beingforwarded over the system bus 242 to the network adapter 210 (and/or thecluster access adapter 212 if sending to another node in the cluster)where the information is formatted into a data packet and returned tothe host device 205 over the network 216 (and/or returned to anothernode attached to the cluster over the cluster fabric 215).

In an embodiment, storage of information on disk arrays 218, 220, 222can be implemented as one or more storage volumes 230, 232 that arecomprised of a cluster of disks 224, 226, 228 defining an overalllogical arrangement of disk space. The disks 224, 226, 228 that compriseone or more volumes are typically organized as one or more groups ofRAIDs. As an example, volume 230 comprises an aggregate of disk arrays218 and 220, which comprise the cluster of disks 224 and 226.

In an embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In an embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In an embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the one or more LUNs 238.

It may be appreciated that replay of metadata and data operations may beimplemented for the data storage system 200. In an example, the node 202may execute operation upon an NVRAM and replay the operations to flushthe NVRAM to storage. It may be appreciated that replay of metadata anddata operations may be implemented for and/or between any type ofcomputing environment, and may be transferrable between physical devices(e.g., node 202, host device 205, a desktop computer, a tablet, alaptop, a wearable device, a mobile device, a storage device, a server,etc.) and/or a cloud computing environment (e.g., remote to the node 202and/or the host device 205).

One embodiment of a synchronous replication based cutover engine isillustrated by an exemplary method 300 of FIG. 3 and further describedin conjunction with system 400 of FIGS. 4A-4D. A first computingenvironment 402 comprises a storage object 404, such as a file, adirectory, a volume, a storage virtual machine, etc., as illustrated byFIG. 4A. In an embodiment, the storage object 404 may comprise a storagevirtual machine of a plurality of volumes storage across multiple nodesof a first cluster. A second computing environment 406 may maintain areplicated storage object 408 as a replication of the storage object404. The replicated storage object 408 may comprise a replicated virtualmachine of a plurality of replicated volumes stored across multiplenodes of a second cluster. A replication process may be used toreplicate data within the storage object 404 and to replicate operationssuch as data operations and metadata operations (e.g., write/modifyoperations) directed to the storage object 404 to the replicated storageobject 408.

A determination may be made that the storage object 404 should bemigrated to the second computing environment 406 as the replicatedstorage object 408. In an embodiment, as part of migration, thereplicated storage object 408 is created within the second computingenvironment 406 and the replication process is performed to replicatedata into the replicated storage object 408. In an embodiment, thedetermination may be made based upon receiving a migration command. Inan embodiment, performance statistics of the first computing environment402 are evaluated against a performance criteria to determine that themigration should be performed based upon the performance statistics notsatisfying the performance criteria. In an embodiment, storage capacitystatistics of the first computing environment 402 are evaluated againsta storage capacity criteria to determine that the migration should beperformed based upon the storage capacity statistics not satisfying thestorage capacity criteria. In this way, the replication process isperformed to migrate the storage object 404 to the second computingenvironment 406 as the replicated storage object 408.

At 302, an asynchronous replication process 410 is executed to performasynchronous incremental transfers of data of the storage object 404from the first computing environment 402 to the replicated storageobject 408 until a cutover criteria is met, as illustrated by FIG. 4A.In an embodiment, the cutover criteria can be defined as a timespan forperforming asynchronous replication (e.g., the cutover criteriacorresponds to a 3 minute timespan during which asynchronous replicationis to be performed). In an embodiment, the cutover criteria can bedefined as an amount of data remaining to be replicated (e.g., thecutover criteria corresponds to a remaining percentage of data to bereplicated such as 5% or a remaining size of data to be replicated suchas 50 megabytes).

At 304, a synchronous replication process 412 is executed tosynchronously replicate operations (e.g., data operations, metadataoperations, write operations, etc.), targeting the storage object 404,to the replicated storage object 408 based upon the cutover criteriahaving been met, as illustrated by FIG. 4B. With synchronousreplication, a client that submitted an operation to the first computingenvironment 402 for execution upon the storage object 404 is notacknowledged as the operation being successful until both the operationand a replicated operation of the operation are acknowledged (e.g., theoperation being committed to the storage object 404 and the secondcomputing environment 406 acknowledging receipt of the replicatedoperation for commitment upon the replicated storage object 408).

In an embodiment of the replication process, operations (e.g., writeoperations) are executed upon the storage object 404 before beingtransmitted as replicated operations to the second computing environment406 for execution upon the replicated storage object 408. The operationsmay be executed according to a defined ordering. Thus, the replicatedoperations are assigned sequence numbers based upon the order ofexecution. The sequence numbers are used by the second computingenvironment 406 to enforce the execution of the replicated operationsupon the replicated storage object 408 according to the definedordering. In particular, the second computing environment 406 maytransmit messages acknowledging receipt of the replicated operations sothat the first computing environment 402 can acknowledge to the clientthat the operations are successful upon commitment to the storage object404. The second computing environment 406 may queue the replicatedoperations into a queue. The second computing environment 406 maysort/order the replicated operations based upon assigned sequencenumbers so that the sorted replicated operations correspond to an orderof execution by the first computing environment 402. In this way, thesecond computing environment 406 can execute the replicated operationsupon the replicated storage object 408 according to a similar order ofexecution.

At 306, a cutover 414 is performed to direct operations (e.g., write andread requests) from targeting the storage object 404 to targeting thereplicated storage object 408 upon completion of the cutover 414, asillustrated by FIGS. 4C and 4D. The cutover 414 is performed based uponthe synchronous replication process reaching a steady state ofsynchronous replication for sub-objects of the storage object 404 (e.g.,files, directories, data blocks, or other sub-objects of a volume or aplurality of volumes of a storage virtual machine). The steady state iswhere operations are committed to both the storage object 404 and thereplicated storage object 408.

In an embodiment of the cutover 414, an application, creating theoperations, is quiesced to pause the application from generatingoperations targeting the storage object 404. A drain operation isperformed to complete pending operations not yet committed to storage(e.g., inflight operations, such as replicated operations not yetcommitted to the replicated storage object 408 by the second computingenvironment). Protocol specific information, such as network file systemlock data and a replay cache of non-idempotent operations, is replicatedto the replicated storage object 408. Because the storage object 404 andthe replicated storage object 408 as in sync from the synchronousreplication process, there is a relatively small number of operations todrain (complete), and thus a time period during which I/O from theapplication is quiesced is short.

In an embodiment of the cutover 414, the cutover 414 is performed once amigration start operation has completed, such as where the asynchronousreplication 410 and synchronous replication 412 have completed. At thispoint, a destination virtual filer unit (e.g., hardware and/or softwareproviding access to the replicated storage object 408, such as a logicalpartition of a storage array that manages one or more virtual internalvolumes comprising the replicated storage object 408) at the secondcomputing environment 406 is accessible, while a source virtual filerunit at the first computing environment 402 is no longer accessible(e.g., hardware and/or software that provided access to the storageobject 404). The cutover 414 can be automatically enabled at the end ofthe start migration operation based upon a data migration operationbeing initiated.

Various verifications are performed before data access is cutover 414 tothe replicated storage object 408 at the second computing environment406. In an embodiment, a verification is performed to verify that IPaddresses of the source virtual filer unit are not in use in a same IPspace in the second computing environment 406. A verification isperformed that no errors occurred in a last update on any replicationrelations, such as a synchronous replication relationship, involved inthe migration of the storage object 404 from the first computingenvironment 402 to the second computing environment 406 as thereplicated storage object 408. A verification is perform that if onlinemigration is not enabled, then applications that use a dataset (e.g.,data within the storage object 404) or one of the virtual filer unitsare shutdown. A verification is performed where if online migration isenabled, then the first computing environment 402 (e.g., a sourcestorage system) and the second computing environment 406 (e.g., adestination storage system) are checked to see if they have areplication license and are executing compatible storage operatingsystem versions.

A verification is performed to verify that the second storageenvironment 406 has licenses for all allowed protocols on thedestination virtual filer unit. A verification is performed to verifythat aggregates hosting destination volumes corresponding to thereplicated storage object 408 have adequate storage space (e.g., forprocessing client writes to the replicated storage object 408). Averification is performed to verify that volumes belonging to the sourcevirtual filer unit have replication relationships, such as synchronousreplication relationships, with the destination volumes.

A verification is performed to verify that CPU utilization of firstcomputing environment 402 (e.g., the source storage system) and thesecond computing environment 406 (e.g., the destination storage system)do not exceed a threshold such as 65 percent. If CPU utilization isbetween the threshold and a second threshold (e.g., between 65 percentand 90 percent), then additional conditions are checked to see whetherthe cutover 414 should proceed, such as whether (1−V)*U+C*V<90 where Vis a percentage of CPU utilization for the second virtual filer unit, Uis CPU utilization of the system (e.g., the first virtual filer unit,the source storage system, the destination storage system, etc.), and Cis a cost factor (e.g., C can have a default value such as 2 and aminimum value such as 1). If CPU utilization exceeds the secondthreshold, such as 90 percent, then a storage management consoleprovisioning capability is invoked to revert all changes, and thus thecutover 414 will have to be restarted. A verification is performed toverify that current disk utilization of selected aggregates on thesecond computing environment 406 do not exceed a third threshold, suchas 70 percent. If one or more of the verifications fail, then thecutover 414 is not performed and an error message is returned.

Once the verifications are passed, the storage management consoleprovisioning capability is executed to change corresponding replicationrelationships to a synchronous mode if virtual filer volumes belongingto dataset with online migration option enabled (e.g., volumescomprising the storage object 404). A script for migration is executed.If the script is specified as part of the destination switch operation(e.g., switching over data access to the replicated storage object 408at the second computing environment 406), then the script is executedbefore the cutover 414 is performed. If the script is specified as partof the destination switch operation and contains cutover operations,then the cutover operations are performed during the cutover 414, whichmay be useful for scripts that quiesce an application. If the script haspost migration operations, the post migration operations are executedafter the cutover 414, which is useful for scripts that resume theapplication.

Data access is then switched from the source virtual filer unit to thedestination virtual filer unit. The source virtual filer unit isdeleted. The new destination virtual filer unit becomes active,writable, and online. The dataset is suspended to prevent new backupsfrom starting during the migration. Volumes are then removed from thesource dataset. As each volume is added to the new destination (e.g., tothe replicated storage object 408 such as to destination virtual filevolumes), corresponding source volumes are removed from the sourcedataset. Dynamic references in the source dataset are not removed, butare removed after a migration cleanup operation completes.

Backup version tables are modified to point to the new destinationprimary storage (e.g., the second computing environment 406 comprisingthe replicated storage object 408). Backup and mirror relationships aremodified to point to the new destination primary storage. History datawithin an operations manager is copied to reflect the new destinationprimary storage. Dataset operations are resumed.

The storage management console provisioning capability is capable ofhandling various failures. If the data migration succeeds but a backuprelationship migration fails (e.g., a migration of a backup relationshipbetween the storage object 404 and a second storage object to beingbetween the replicated storage object 408 and the second storageobject), then the dataset remains in a suspended mode with a migratedwith errors status. Such errors may be manually corrected. Oncecorrected, the migration status is changed to normal and datasetoperations are resumed. If the migration cutover 414 fails, the sourcevirtual filer unit is brought back online. The status of the sourcedataset and virtual filer unit is set to a migrated failed status. Thedestination storage, such as the replicated storage object 408, isdestroyed. If either the source or destination virtual filer unitcrashes, the cutover 414 is aborted. All changes done so far arereverted, and performance monitoring is stopped.

Once the cutover 414 is complete, the application and/or other remotedevices are now switched over to accessing the replicated storage object408 instead of the storage object 404. Any applications that wereshutdown are restarted. In this way, the client I/O 401 is redirected tothe replicated storage object 408 at the second computing environment406. If a failure to migrate the storage object 404 occurs, then asnapshot created by a last asynchronous incremental transfer is used toperform a rollback of the replicated storage object 408 to a state whenthe last asynchronous incremental transfer was performed. That is, thesnapshot is used to modify the replicated storage object 408 to comprisedata that the replicated storage object 408 comprised after the lastasynchronous incremental transfer was performed for the replicatedstorage object 408.

In an embodiment, a timestamp matching process is performed to matchtimestamps of filesystem modification operations to metadata of thefirst computing environment 402 and the second computing environment406. In an embodiment of the timestamp matching process, synchronousreplication processes incoming operations in a sequential manner (e.g.,operations are processed on a primary storage object first and are thenreplicated to a secondary storage object).

A primary filesystem, as part of processing the operation, will modifyvarious timestamps pertaining to the storage object (e.g., an inode)such as mtime (a modification time), ctime (a status change time) andcrtime (a creation time). As a response to the operation, synchronousreplication will obtain the modified timestamp (mtime). The synchronousreplication will replicate the modified timestamp to the secondarystorage object. This works fine when operations are processed in serialfashion, such as where each operation is written to the primary storageobject first and is then written to the secondary storage object. Butthis may not be used as the mode of operation due to performanceconsiderations hence data operations are processed in parallel (e.g.,multiple write operations can be executed in parallel albeit insequential manner). Since the order of operations is not maintained atthe second computing environment 406, the order of operations beingexecuted upon the primary storage object and the secondary storageobject can be different. This can result in timestamps not matchingbetween the primary storage object and the secondary storage. A way tofix this inconsistency is to teach the filesystem to not modifytimestamp when the current timestamp on an inode is already higher thanthe current operation's timestamp.

In an embodiment, a method comprises performing a timestamp matchingprocess to match timestamps of filesystem modification operations tometadata of the first computing environment 402 and the second computingenvironment 406. In an embodiment, the method comprises evaluatingperformance statistics of the first computing environment 402 against aperformance criteria to determine that the storage object 404 is to bemigrated to the second computing environment 406 as the replicatedstorage object 408 based upon the performance statistics being less thanthe performance criteria. In an embodiment, the method comprisesevaluating storage capacity statistics of the first computingenvironment 402 against a capacity criteria to determine that thestorage object 404 is to be migrated to the second computing environment406 as the replicated storage object 408 based upon the storage capacitystatistics being less than the capacity criteria.

In an embodiment, the method comprise executing operations upon thestorage object 404 before transmitting replicated operations of theoperations to the second computing environment 406 for execution uponthe replicated storage object 408 and comprises executing the operationsaccording to a defined ordering and assigning sequence numbers to thereplicated operations for enforcement by the second computingenvironment 406 for executing the replicated operations according thedefined ordering based upon the sequence numbers. In an embodiment, themethod comprises performing a rollback of the replicated storage object408 using a snapshot created by a last asynchronous incremental transferbased upon detecting a failure to migrate the storage object to thesecond computing environment 406 as the replicated storage object 408.

Still another embodiment involves a computer-readable medium comprisingprocessor-executable instructions configured to implement one or more ofthe techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 5, wherein the implementationcomprises a computer-readable medium 508, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 506. This computer-readable data 506, such asbinary data comprising at least one of a zero or a one, in turncomprises a processor-executable computer instructions 504 configured tooperate according to one or more of the principles set forth herein. Insome embodiments, the processor-executable computer instructions 504 areconfigured to perform a method 502, such as at least some of theexemplary method 300 of FIG. 3, for example. In some embodiments, theprocessor-executable computer instructions 504 are configured toimplement a system, such as at least some of the exemplary system 400 ofFIGS. 4A-4D, for example. Many such computer-readable media arecontemplated to operate in accordance with the techniques presentedherein.

FIG. 6 is a diagram illustrating an example operating environment 600 inwhich an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 628, such as a laptop, tablet,personal computer, mobile device, wearable device, etc. In anotherexample, the techniques described herein may be implemented within astorage controller 630, such as a node configured to manage the storageand access to data on behalf of the client device 628 and/or otherclient devices. In another example, the techniques described herein maybe implemented within a distributed computing platform 602 such as acloud computing environment (e.g., a cloud storage environment, amulti-tenant platform, etc.) configured to manage the storage and accessto data on behalf of the client device 628 and/or other client devices.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 628, the storagecontroller 630, and the distributed computing platform 602. For example,the client device 628 may transmit operations, such as data operationsto read data and write data and metadata operations (e.g., a create fileoperation, a rename directory operation, a resize operation, a setattribute operation, etc.), over a network 626 to the storage controller630 for implementation by the storage controller 630 upon storage. Thestorage controller 630 may store data associated with the operationswithin volumes or other data objects/structures hosted within locallyattached storage, remote storage hosted by other computing devicesaccessible over the network 626, storage provided by the distributedcomputing platform 602, etc. The storage controller 630 may replicatethe data and/or the operations to other computing devices so that one ormore replicas, such as a destination storage volume that is maintainedas a replica of a source storage volume, are maintained. Such replicascan be used for disaster recovery and failover.

The storage controller 630 may store the data or a portion thereofwithin storage hosted by the distributed computing platform 602 bytransmitting the data to the distributed computing platform 602. In oneexample, the storage controller 630 may locally store frequentlyaccessed data within locally attached storage. Less frequently accesseddata may be transmitted to the distributed computing platform 602 forstorage within a data storage tier 608. The data storage tier 608 maystore data within a service data store 620, and may store clientspecific data within client data stores assigned to such clients such asa client (1) data store 622 used to store data of a client (1) and aclient (N) data store 624 used to store data of a client (N). The datastores may be physical storage devices or may be defined as logicalstorage, such as a virtual volume, LUNs, or other logical organizationsof data that can be defined across one or more physical storage devices.In another example, the storage controller 630 transmits and stores allclient data to the distributed computing platform 602. In yet anotherexample, the client device 628 transmits and stores the data directly tothe distributed computing platform 602 without the use of the storagecontroller 630.

The management of storage and access to data can be performed by one ormore storage virtual machines (SMVs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 628,within the storage controller 630, or within the distributed computingplatform 602 such as by the application server tier 606. In anotherexample, one or more SVMs may be hosted across one or more of the clientdevice 628, the storage controller 630, and the distributed computingplatform 602.

In one example of the distributed computing platform 602, one or moreSVMs may be hosted by the application server tier 606. For example, aserver (1) 616 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 622. Thus, an SVM executingon the server (1) 616 may receive data and/or operations from the clientdevice 628 and/or the storage controller 630 over the network 626. TheSVM executes a storage application to process the operations and/orstore the data within the client (1) data store 622. The SVM maytransmit a response back to the client device 628 and/or the storagecontroller 630 over the network 626, such as a success message or anerror message. In this way, the application server tier 606 may hostSVMs, services, and/or other storage applications using the server (1)616, the server (N) 618, etc.

A user interface tier 604 of the distributed computing platform 602 mayprovide the client device 628 and/or the storage controller 630 withaccess to user interfaces associated with the storage and access of dataand/or other services provided by the distributed computing platform602. In an example, a service user interface 610 may be accessible fromthe distributed computing platform 602 for accessing services subscribedto by clients and/or storage controllers, such as data replicationservices, application hosting services, data security services, humanresource services, warehouse tracking services, accounting services,etc. For example, client user interfaces may be provided tocorresponding clients, such as a client (1) user interface 612, a client(N) user interface 614, etc. The client (1) can access various servicesand resources subscribed to by the client (1) through the client (1)user interface 612, such as access to a web service, a developmentenvironment, a human resource application, a warehouse trackingapplication, and/or other services and resources provided by theapplication server tier 606, which may use data stored within the datastorage tier 608.

The client device 628 and/or the storage controller 630 may subscribe tocertain types and amounts of services and resources provided by thedistributed computing platform 602. For example, the client device 628may establish a subscription to have access to three virtual machines, acertain amount of storage, a certain type/amount of data redundancy, acertain type/amount of data security, certain service level agreements(SLAs) and service level objectives (SLOs), latency guarantees,bandwidth guarantees, access to execute or host certain applications,etc. Similarly, the storage controller 630 can establish a subscriptionto have access to certain services and resources of the distributedcomputing platform 602.

As shown, a variety of clients, such as the client device 628 and thestorage controller 630, incorporating and/or incorporated into a varietyof computing devices may communicate with the distributed computingplatform 602 through one or more networks, such as the network 626. Forexample, a client may incorporate and/or be incorporated into a clientapplication (e.g., software) implemented at least in part by one or moreof the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, storagecontrollers, laptop computers, notebook computers, tablet computers orpersonal digital assistants (PDAs), smart phones, cell phones, andconsumer electronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 602, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 604, theapplication server tier 606, and a data storage tier 608. The userinterface tier 604 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 610 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements,which may be accessed via one or more APIs.

The service user interface 610 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 602, such asaccessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 608 may include one or more data stores, which mayinclude the service data store 620 and one or more client data stores.Each client data store may contain tenant-specific data that is used aspart of providing a range of tenant-specific business and storageservices or functions, including but not limited to ERP, CRM, eCommerce,Human Resources management, payroll, storage services, etc. Data storesmay be implemented with any suitable data storage technology, includingstructured query language (SQL) based relational database managementsystems (RDBMS), file systems hosted by operating systems, objectstorage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 602 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, In anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on). In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: asynchronously replicatingdata of a storage object hosted by a first node to a replicated storageobject hosted by a second node; synchronously replicating operations,targeting the storage object, to the replicated storage object, whereinreplicated operations targeting the replicated storage object areterminated upon the second node receiving the replicated operations; andredirecting operations from targeting the storage object to targetingthe replicated storage object based upon the storage object and thereplicated storage object reaching a steady state of synchronousreplication.
 2. The method of claim 1, wherein the replicated operationsare committed by the second node as a background process.
 3. The methodof claim 1, wherein a replicated operation is a replica of an operation,and the method comprising: transmitting the replicated operation to thesecond node based upon the operation successfully being executed uponthe storage object.
 4. The method of claim 1, comprising: executing theoperations upon the storage object according to a defined ordering. 5.The method of claim 4, comprising: assigning sequence numbers to thereplicated operations based upon the defined ordering.
 6. The method ofclaim 5, wherein the sequence numbers are used by the second node forexecuting the replicated operations according to the defined orderingbased upon the sequence numbers.
 7. The method of claim 1, comprising:matching timestamps of file system modification operations to metadataof the first node.
 8. The method of claim 1, comprising: matchingtimestamps of file system modification operations to metadata of thesecond node.
 9. The method of claim 1, comprising: synchronouslyreplicating, by a synchronous replication process, data operations andmetadata operations.
 10. The method of claim 9, wherein the synchronousreplication process is performed after an asynchronous replicationprocess that asynchronously replicates the data of the storage object tothe replicated storage object until a cutover criteria is met.
 11. Themethod of claim 1, comprising: synchronously replicating a modifiedtimestamp of the storage object to the replicated storage object basedupon operations and replicated operations being executed in a serialfashion.
 12. The method of claim 1, comprising: determining that atimestamp of the replicated storage object is different than a timestampof the storage object based upon operations and replicated operationsbeing executed out of order.
 13. The method of claim 12, comprising:refraining from modifying a timestamp of the storage object based upon acurrent timestamp of an inode of the storage object being larger than atimestamp of a current operation being executed.
 14. A non-transitorymachine readable medium comprising instructions for performing a method,which when executed by a machine, causes the machine to: asynchronouslyreplicate data of a storage object hosted by a first node to areplicated storage object hosted by a second node; synchronouslyreplicate operations, targeting the storage object, to the replicatedstorage object, wherein replicated operations targeting the replicatedstorage object are terminated upon the second node receiving thereplicated operations; and redirect operations from targeting thestorage object to targeting the replicated storage object based upon thestorage object and the replicated storage object reaching a steady stateof synchronous replication.
 15. The non-transitory machine readablemedium of claim 14, wherein the replicated operations are committed bythe second node as a background process.
 16. The non-transitory machinereadable medium of claim 14, wherein the storage object comprises aplurality of volumes of a storage virtual machine and the replicatedstorage object comprises a plurality of replicated volumes of areplicated virtual machine.
 17. The non-transitory machine readablemedium of claim 16, wherein an asynchronous process and a synchronousprocess replicates data and operations, associated with the plurality ofvolumes, to the plurality of replicated volumes.
 18. A computing devicecomprising: a memory comprising machine executable code for performing amethod; and a processor coupled to the memory, the processor configuredto execute the machine executable code to cause the processor to:asynchronously replicate data of a storage object hosted by a first nodeto a replicated storage object hosted by a second node; synchronouslyreplicate operations, targeting the storage object, to the replicatedstorage object, wherein replicated operations targeting the replicatedstorage object are terminated upon the second node receiving thereplicated operations; and redirect operations from targeting thestorage object to targeting the replicated storage object based upon thestorage object and the replicated storage object reaching a steady stateof synchronous replication.
 19. The computing device of claim 18,wherein the replicated operations are committed by the second node as abackground process.
 20. The computing device of claim 18, wherein themachine executable code causes the processor to: match timestamps offile system modification operations to metadata of the first node andthe second node.